1. Field of the Invention
This invention relates to a part of an office machine, and more particularly to a knuckle arm that interconnects a machine body and a top cover of an office machine.
2. Description of the Related Art
Two knuckle arms are typically disposed between a top cover and a machine body of an office machine, such as a copier, or scanner, for use in the opening and closing of the top cover relative to the machine body. Referring to FIG. 1, a conventional knuckle arm 10, which is disclosed in U.S. Pat. No. 6,456,365, is shown to include a mounting seat 11 fixed on a machine body 21 of an office machine 20, a connecting seat 12 disposed pivotally on the mounting seat 11, a bottom cam sliding seat 13 disposed slidably within the connecting seat 12, a top cam sliding seat 14 disposed slidably within the connecting seat 12 and located above the bottom cam sliding seat 13, a compression spring 15 disposed between the bottom and top cam sliding seats 13, 14, a lifting seat 16 disposed pivotally on the connecting seat 12 and connected fixedly to a top cover 22 of the office machine 20, a bottom pivot rod 17 extending through the mounting seat 11 and the connecting seat 12 and kept in contact with a cam edge 131 of the bottom cam sliding seat 13, and a top pivot rod 18 extending through the connecting seat 12 and kept in contact with a cam edge 141 of the top cam sliding seat 14.
As such, a force can be applied to the top cover 22 so as to open and close the top cover 22 relative to the machine body 21. Although the knuckle arm 10 can achieve its intended purposes, in actual use, it suffers from the following disadvantages:
(1) The knuckle arm 10 has a substantial number of components, and therefore is bulky.
(2) There is a need for high precision during manufacture of the cam edges 131, 141 of the bottom and top cam sliding seats 13, 14. The processes required to achieve such high precision, particularly in consideration of the fact that the shapes of the cam edges 131, 141 are different, ultimately result in high manufacturing and design costs of the knuckle arm 10.
(3) During assembly, it is necessary to press the compression spring 15 toward the bottom sliding seat 13 just before the top pivot rod 18 is inserted into the connecting seat 12 and the lifting seat 16. The compression spring 15 has a large spring force that is difficult to overcome.